This invention relates to a method for the manufacture of a foamed article of poly-n-butyl methacrylate or a foamed article of a copolymer of n-butyl methacrylate and other vinyl monomer, which foamed article is free from the possibility of causing environmental pollution.
To date, foamed articles of numerous high molecular compounds have been developed and have found acceptance for use in heat insulation materials, packaging materials, and noise-abating materials. These conventional foamed articles have had various disadvantages such as highly complicated methods which are inevitably required for their production and very serious problems of environmental pollution caused by the noxious gases they generate during combustion. For example, a foamed polystyrene article is manufactured by blending a polystyrene resin and an expanding agent and heating the resultant blend at a temperature higher than the decomposition temperature of the expanding agent. Thus, the manufacture of this article requires steps for the blending of the expanding agent and the application of heat to the resultant blend, making the procedure of manufacture highly complicated and consequently elevating the cost of production. In the case of a foamed polyurethane article, although it can be produced in the neighborhood of room temperature without requiring incorporation of any expanding agent, it has a problem that the foamed article emits a noxious gas during its combustion.
Japanese Unexamined Patent Publication No. 67358/1973 discloses a method for producing a foamed article of a high molecular organic compound having fine cells uniformly distributed therein by polymerizing a vinyl-polymeric unsaturated carboxylate. In the disclosure, butyl methacrylate is cited as one example of vinyl-polymeric unsaturated carboxylates. This method is characterized by heating the carboxylate in the presence of a halogenide of a metallic element from the 4th and 5th periods in the Periodic Table of Elements and particularly by effecting this heating at a temperature higher than the melting point of the high molecular organic compound.
The object of this invention is to provide a method for the manufacture of a foamed article of poly-n-butyl methacrylate or a foamed article of a copolymer of not less than 95% of n-butyl methacrylate and not more than 5 percent of other vinyl monomer (such as styrene, methyl methacrylate, divinyl adipate, for example) by an easy method which requires neither addition of any expanding agent nor application of heat).